Abstract: For analyzing the influence of aggregate gradation on the concrete behavior, the grain-spring model of discrete element method is presented. Taking aggregates randomly distributed in the concrete as rigid grains and mortar between aggregates as springs, the grain-spring model is established in mesoscale. The stress-strain relationship and rupture surface of concrete having different aggregate gradation under compression are calculated. The calculated results are identical in many aspects with the results of experimentation. The results show that the grain-spring model in mesoscale can be used to analyze the influence of aggregate gradation on the macroscale behavior of concrete. And in the plane problem, the element stiffness matrix of the grain-spring model is 6×6. The quantity of storage and calculation is very smaller than that of the finite element method.